Porous membranes are typically sheets of preselected material having certain characteristics that are optimal for a particular application. For example, porous membranes made of polymers are often used to filter solids from liquids. Recently, thin porous membranes made of polytetrafluoroethylene, PTFE, having the characteristic of being hydrophobic, have been found to be suitable for use in certain scientific laboratory apparatuses to prevent the passage of water while allowing other liquids to pass through the membrane. An apparatus referred to as a liquid-liquid hydrophobic concentrator/extractor is one such apparatus that employs a thin hydrophobic PTFE membrane to block the passage of water in one section of the apparatus while allowing other liquids, such as organic solvents, to pass downstream to other sections of the apparatus for subsequent processing.
A problem encountered with using porous PTFE membranes in laboratory apparatuses is the membrane is typically very thin and fragile making it prone to being damaged while being transported, stored, and handled. The thin fragile membrane is thus difficult to install in apparatuses such as the above discussed hydrophobic concentrator/extractor without damaging or mis-positioning the membrane. The additional care and time taken to install the membrane in an apparatus leads to extra expenses for a laboratory, especially if the laboratory has a limited number of such apparatuses. An additional problem with using porous PTFE membranes in various apparatus is the porous membranes have a tendency to wick liquids to the periphery of the membrane and beyond the clamped joint, or coupling, in which the membrane is installed. Thus, the wicking tendency makes it difficult to obtain an adequate seal about the membrane without possibly over stressing the joint, the clamping mechanism, or the surrounding structure of the apparatus containing the membrane.
There are various known methods of sealing, or bonding, gaskets about thin porous membranes to facilitate handling and sealing of the membrane within an accommodating apparatus. Such methods include bonding the periphery of the membrane to the gasket by the application of adhesives to regions common to the membrane and the gasket. However, the use of such adhesives on membranes positioned in apparatuses in which organic solvents are used for processing liquid samples, such as a liquid-liquid concentrator/extractor apparatus, may cause the adhesive to degrade and contaminate the fluids being processed within the apparatus.
It is also known that polymer membranes may be sealed to polymer gaskets by applying sufficient heat to a preselected common region of the membrane and the gasket to form a fused bond therebetween. However, the amount of heat applied to the region must be carefully controlled so as not to exceed the optimal heat sealing temperatures of the membrane and/or the gasket.